Using the recent technique of fracture-labelling (developed in our laboratory) in which cytochemical studies are performed on cells that have been previously freeze-fractured, we determined the partition and the distribution of Wheat Germ Agglutinin (WGA) and Concanavalin A (Con A) receptors in freeze-fractured plasma membranes of platelets from normal donors and from patients with Glanzmann's thrombasthenia (GT) and Bernard-Soulier Syndrome (BSS).